Are lichens active under snow in continental Antarctica?

Abstract

Photosynthetic activity, detected as chlorophyll a fluorescence, was measured for lichens under undisturbed snow in continental Antarctica using fibre optics. The fibre optics had been buried by winter snowfall after being put in place the previous year under snow-free conditions. The fibre optics were fixed in place using specially designed holding devices so that the fibre ends were in close proximity to selected lichens. Several temperature and PPFD (photosynthetic photon flux density) sensors were also installed in or close to the lichens. By attaching a chlorophyll a fluorometer to the previously placed fibre optics it proved possible to measure in vivo potential photosynthetic activity of continental Antarctic lichens under undisturbed snow. The snow cover proved to be a very good insulator for the mosses and lichens but, in contrast to the situation reported for the maritime Antarctic, it retained the severe cold of the winter and prevented early warming. Therefore, the lichens and mosses under snow were kept inactive at subzero temperatures for a prolonged time, even though the external ambient air temperatures would have allowed metabolic activity. The results suggest that the major activity period of the lichens was at the time of final disappearance of the snow and lasted about 10-14 days. The activation of lichens under snow by high air humidity appeared to be very variable and species specific. Xanthoria mawsonii was activated at temperatures below -10 degrees C through absorption of water from high air humidity. Physcia dubia showed some activation at temperatures around -5 degrees C but only became fully activated at thallus temperatures of 0 degrees C through liquid water. Candelariella flava stayed inactive until thallus temperatures close to zero indicated that liquid water had become available. Although the snow cover represented the major water supply for the lichens, lichens only became active for a brief time at or close to the time the snow disappeared. The snow did not provide a protected environment, as reported for alpine habitats, but appeared to limit lichen activity. This provides at least one explanation for the observed negative effect of extended snow cover on lichen growth.

Habitat stress initiates changes in composition, CO2 gas exchange and C-allocation as life traits in biological soil crusts

“…being activated by water uptake in the gaseous phase from snow at subzero temperatures. Nevertheless, there is little evidence that activation by water vapour occurs naturally in Antarctica (Hovenden et al, 1994;Pannewitz et al, 2003). Here, we found that the BSC from Site Darwin dominated by the green algal lichen Acarospora gwynnii did not reactivate from water vapour alone.…”

Earth as a Tool for Astrobiology—A European Perspective

“…One example used in ecological field campaigns are the measurements on metabolic activity such as measuring methane production by methanogens (Wagner et al 2005(Wagner et al , 2007 or photosynthetic activity by phototrophs like cyanobacteria, alga and lichens (Lange 1969;Lange et al 1970;Schroeter et al 1994;Schroeter and Scheidegger 1995;Pannewitz et al 2003). Also, reproduction expressed by the growth rate may be recorded, which might take several years of continuously monitoring the selected field sites in order to obtain measurement results over longer time scales.…”

Estimating global carbon uptake by lichens and bryophytes with a process-based model

“…Furthermore, it changes the dynamics of the water supply and the temperature regime compared to a situation without snow cover. It is assumed in the model that lichens and bryophytes are not able to photosynthesise if the snow cover above them exceeds a certain critical thickness p snow (Pannewitz et al, 2003). Since it is impractical to simulate the water content of the organisms under snow, dark respiration is also assumed to be negligible in this situation.…”